New Jersey governor Chris Christie outlines plans for a special election to be held to fill the US Senate seat of Frank Lautenberg. Photograph: Jeff Zelevansky/Getty Images

The governor of New Jersey, Chris Christie, on Tuesday announced a special election, to be held in October, to fill the US Senate seat left vacant by the late Frank Lautenberg.

Declaring that New Jersey voters deserve "a choice and a voice", Christie said primary elections would be held in August and a general election on 16 October. The governor did not name an appointment to hold the seat through October, saying he had "yet to make a determination". He is expected to name a fellow Republican. Lautenberg, 89, a five-term Democratic senator, died on Monday, of pneumonia.

Christie presented the October election as the best way to ensure that the state would be fully represented in the Senate as soon as possible. "The issues facing the US senate are too critically important not to have an elected representative making those decisions," he said. "We have to move to swiftly to fill this seat, to make sure there is a primary and an election as soon as possible."

Christie could have simply appointed a senator to hold the seat until it came up for election on schedule, in November 2014. Doing so, however, would have risked charges of delay from Democrats and damage to his national standing – a matter of importance for a potential 2016 presidential candidate.

Christie could also have added the election for Lautenberg's seat to the list of November 2013 contests, when he will stand for re-election as governor. But that arrangement would have had him running in an election when turnout among Democrats could surge in support of the popular mayor of Newark, Cory Booker, who is positioned to run for Lautenberg's seat. The added Democrats could have endangered the popular Christie's chances of re-election.

Christie said on Tuesday that the second option, adding the vacant Senate seat to the slate on Election Day 2013, was not permitted by state law. "I deem it advisable to have a special election," he said. "In fact I deem it necessary. The dates are what the statute requires."

Christie dismissed the idea that it would be too costly to mount two special elections when other options were available. The state election law-enforcement commission has estimated that statewide elections cost $12.2m apiece. "I don't know what the cost is, and quite frankly, I don't care," Christie said. "We're not going to be penny wise and pound foolish around here."

Christie likewise denied that his decision had been informed by political calculations. "I'm not going to play politics with this," he said, arguing that waiting until November 2014 for an election was not an option. "Eighteen months is a long time, and there's going to be a lot of consequential issues being decided … I believe the people have to decide."

The Senate is preparing for a showdown over judicial appointments, a round of budget deadlines and a renewed debate over the filibuster. Immigration reform, expected to come to a vote this summer, is seen as having sufficient bipartisan support to pass. If Christie appoints a Republican, Democrats would retain a 54-46 majority, counting the votes of two independents.

"I have yet to make a determination as to who I will appoint to hold this seat … but when I determine who that person is I will make that announcement," Christie said. "I do have a preference for one party over the other so that may color my judgment a little."